(1) Field of the Invention
This invention relates to microchip capacitors, and more particularly to microchip capacitors used as circuit elements in internal impedance matching circuits of microwave transistors.
(2) Description of the Related Art
A prior art microchip capacitor of the kind to which the present invention relates is shown in FIG. 1. In this microchip capacitor, one or more metallized patterns 8 are provided on the principal front surface of a dielectric substrate 1, and the principal back surface thereof is entirely metallized.
FIG. 2 shows another example of prior art microchip capacitors. In this microchip capacitor, the principal front surface of a dielectric substrate 1 is provided with one or more first metallized patterns 2 and also provided with second metallized patterns 3 each for a plurality of first metallized patterns 2, the principal back surface of the substrate being fully metallized.
In operation, both the capacitors of FIG. 1 and FIG. 2 function as parallel flat layer capacitor. Particularly, in the microchip capacitor of FIG. 2, two different capacitances are provided in a single dielectric substrate 1 by the first and second metallized patterns 2 and 3.
FIG. 3 illustrates the use of the microchip capacitor of FIG. 2 as circuit constants of an internal impedance matching circuit of a microwave transistor. Transistor chips in the microwave transistor 2 and the first metallized patterns 2 of the microchip capacitor are connected to one another by bonding wires 7. Also, the first and second metallized patterns 2 and 3 on the microchip capacitor are connected to one another by the bonding wires 7.
FIG. 4 is a circuit diagram showing an equivalent electric circuit of the structure shown in FIG. 3. The first and second metallized patterns 2 and 3 of the microchip capacitor function as capacitances C1 and C2, while the bonding wires function as inductances L1 and L2.
In the above prior art microchip capacitor, however, if there occur variations in the internal impedances of the bonding wires 7 connected to the individual electrode patterns and the microwave transistor 6, the load impedances connected to the individual electrodes will become unbalanced among the individual electrodes, and this causes the occurrence of interference resulting in operational instability, such as abnormal oscillation, of the microwave transistor.